Aluminium base alloy



ALuMrNrrnvr sass ALLOY Harold Ernest Greshm, Little Eaton, Alec GeorgeFarrisworth, Derby, and Douglas Wilson Hall, West Monkseaton,Northumberland, England, assiguors to Rolls- Royce Limited, Derby,England, a corporation of Great Britain No Drawing. Application April28, 1954, Serial No. 426,292

Claims priority, application Great Britain July 18, 1949 12 Claims. (CI.75-144) This invention relates to a form of aluminium base alloy whichpossesses a high stress-to-fracture characteristic at 300 C. combinedwith the ability to form sound castings when poured into a sand mouldand to be forgeable from cast ingots.

This application is a continuation-in-part of copending applicationSerial No. 173,244, filed July 11, 1950, now abandoned.

The compressor casings of internal combustion turbine engine are usuallycast in two halves, each half being a very large and complicatedcasting. The compressor rotor blades run at very high speed in closelyspaced relation to elements of the casing. A typical structure involvedis illustrated in U. S. Patent No. 2,543,355. Such a casing structure inpractice may be of the order of 2 ft. 6 ins. in diameter and 2 ft. 6ins. in length. To cast an article of this kind, the mould must be ofextremely intricate shape and it is essential to successful productionthat the alloy should, among other things, have the property ofcompletely filling such a mould without formation of blow holes, hottears or shrinkage cavities in the casting. The blades used in suchrotors are, at least in their profile portion, commonly forged to sizein order to avoid machining, and it is essential that the alloy used forsuch blades should have good forging characteristics, that is, ductilityand hot-workability without loss of high-temperature properties.

Prior to the making of the present mventlon, successive changes andimprovements in the design of internal combustion turbine engines haveincreased the stress upon the casing and the blades, and raised therunning temperature of the compressed air to temperatures of 300 C. andabove. Since the compressor casing comprises a major portion of the massof an internal combustion turbine engine, it has been deemed importantthat such casing be made of a light metal, preferably aluminium or analuminium base alloy having the requisite life at high temperature. Forthis purpose aluminium base alloys have been developed, having invarying degrees some of the desired properties.

When internal combustion turbine engines for aircraft propulsionpurposes were first developed, the compressor casings were made of analuminium base alloy generally as described in the Hall Patent No.1,782,300 of 1930. which alloy had originally been developed for use inautomobile cylinder heads and had excellent casting properties. However,this alloy could not be used when the running temperature of thecompressor in internal combustion turbine engines was raised above about200 C. Commercial specimens of this alloy have a stress-tofracturecharacteristic (in 100 hours at 300 C.) of about 4000 lbs. per squareinch.

Modern compressors running at about 300 C. require a stress-to-fracturecharacteristic in both casing and blades of at least 9000 lbs. persquare inch, and no aluminium base alloy having this characteristic hashereited States Patent tofore been known. Accordingly, for some years,and until the present invention was made, certain compressor casingsdesigned to run at temperatures upwards of 200 C. were made with aforward and cooler portion of aluminium or aluminium base alloy, and anaft and hotter portion of steel or the like. This construction addsmaterially to the weight of the engine for a given horsepower andintroduces problems of differential expansion at the joint between thetwo portions of the casing.

So far as blades were concerned, the problem of life at elevatedtemperature was partially met by use of the aluminium base alloy in theparticular heat-treated and direct chill-cast condition described inHall Patent No. 2,522,575 dating from 1948, but that alloy does notpossess the castability required for making complicated sand-castcompressor casings. Furthermore, blades made of the last-mentioned alloydo not have a sufliciently high stress-to-fracture characteristic at 300C. to permit their use throughout all the rotor stages of moderncompressors.

The object of the present invention is to produce an aluminium basealloy having a stress-to-fracture characteristic (in hours at 300 C.) inexcess of 9000 lbs. per sq. inch and possessing the smooth flowingcharacteristics which produce in the mould a sound casting free of blowholes, hot shortness and shrinkage cavities, thusenabling the two halvesof compressor casings to be made in a single piece from front to rear ofthe compressor casing, which simplifies manufacture and avoids questionsof difiierential expansion.

Alloys according to the present invention have a stress-to-fracturecharacteristic (in 100 hours at 300 C.) in excess of 9000 lbs. per sq.inch and may be produced having such characteristic at 9500 lbs. per sq.inch and higher, such alloy possessing both of the qualities of ease ofcastability and of forgeability. According to a modification of theinvention, in which zirconium is added, the stress-to-fracturecharacteristics of the alloy may be increased to more than 11,000 lbs.per sq. inch.

A further object of the present invention is to produce an aluminiumbase alloy having a stress-to-fracture characteristic (in 100 hours at300 C.) in excess of 9000 lbs. per sq. inch, and also possessing goodforging characteristics thus enabling compressor blades to be forged tosize in at least their profile portion. Such blade meet the designrequirements for compressor blading in later stages of moderncompressors.

All ranges given throughout this specification are percentages by weightof the alloy. Where it is specified that the alloy consist of certainnamed ingredients with the balance essentially aluminium the intentionis to include, in addition to pure aluminium, such impurities and otheringredients as do not materially affect the physical characteristics ofthe alloy and to exclude those which markedly alter the said physicalcharacteristics especially its high temperature stress-to-fractureproperties and its ability to produce in a sand mould a sound castingnormally free of the defects mentioned above.

A good casting alloy, according to the present invention, may be foundwithin the following range:

Approximately, percent Among the impurities which may be present withoutdetriment to the performance of the alloy are up to about 2% zinc, up toabout 0.30% bismuth, up to about 0.20% magnesium, and up to about 1.5%iron.

This alloy may be used in the as cast and aged condition. When solutionheat treated after casting, for example at 530 to 535 or 545 for V2 to20 hours, then quenched in boiling water or oil at 80 C. and finallyaged at 200 to 300 C., this alloy has excellent stressto-fracturecharacteristics at high temperature, as shown by the examples below.

The alloy may also be forged, and after forging should be solution heattreated, for example at 530 to 565 C. for /2 to 20 hours, and then aged.

The amounts of the several ingredients of the compo-- sition may bevaried above or below the amounts specified above, with the resultsindicated generally as follows:

Cpper.-While copper is preferably kept above about 4.9%, it may be usedin slightly lesser amounts in alloys intended for use in the as castcondition. Below about 4.5% there is some detectable reduction in thestress-tofracture characteristic though it remains good for somepurposes down to about 3.5%. When the copper exceeds about 6.2%, thereis a liability to segregation when the alloy is used in ordinary sandcasting though, if the alloy is to be direct chill-cast and then forged,copper can go up to 7% without serious segregation. in alloys forforging, the copper can safely be as high as 7% if desired. Thepreferred amounts are between about 4.9% and 6.2%.

Nickel.-While for some purposes nickel may be used in amounts less thanabout 0.90%, a loss in the stress-tofracture characteristic begins to bedetectable below about 0.90%, though the alloy remains useful for somepurposes down to about 0.50%. When nickel is more than about 1.5 thealloy has a tendency to become brittle, i. e., less ductile when cold.But if some brittleness can be tolerated, the nickel can go up to asmuch as 2%, at which level the stress-to-fracture characteristic isstill very good. The preferred amounts are between about 0.90% and 1.2%.

Titanium.The presence of titanium is essential for the development of ahigh stress-to-fracture characteristic. It also serves as a cleanser andrefiner. However, titanium cannot be used in amounts exceeding about0.30%, owing to a tendency to segregation. The preferred amounts arebetween about 0.10% and 0.25%.

Manganese.Manganese is essential for high stress-tofracturecharacteristics. When used in amounts exceeding approximately 0.60%,there is a tendency to embrittlement and segregation. The preferredamounts are between about 0.20% and 0.30%.

Silic0n.Silicon, in the amount contemplated here, is a normal impurity.It should be kept as low as possible. preferably at or below about0.20%. In amounts above about 0.45% of silicon, there is a seriousfalling otf in the stress-to-fracture characteristic of alloy. It is tobe noted that the normal amount of silicon, around 1.5% to 2%,heretofore commonly used in aluminium base alloys because of its abilityto make the alloy' smoothflowing and castable, is not used for thispurpose at all in the alloy according to the present invention.

C0balt.-Cobalt is an essential ingredient in alloys of the presentinvention, serving both as replacement for silicon in prior knownaluminium base alloys, in which capacity it appears to confer upon thealloy the property of completely filling a sand mould without formationof blow holes, hot tears, or shrinkage cavities, and also serving as themeans by which the stress-to-fracture characteristic of the alloy (in100 hours at 300 C.) is raised to and above 9000 lbs. per sq. inch.Cobalt should preferably be present in amounts between about 0.20% and0.30%, but may be present in amounts up to about 0.50% without detrimentto the qualities of the alloy.

Antim0ny.-Antimony is an optional addition which may be included withcobalt, and is preferably so included in alloys intended for use in sandcastings, since it appears to improve somewhat the casting properties ofthe alloy containing it in theamounts here specified. Antimony shouldpreferably be present in amounts between about 0.10% and 0.30%, but maybe present in amounts up to about 0.50%. If both cobalt and antimony arepresent, their sum should not in any event exceed about 0.60%, sinceabove this amount there is a tendency to segregation, embrittlement andloss of stressto-fracture characteristic. The preferred amount is about0.25% of cobalt and 0.25% of antimony, though excellent results havebeen obtained with 0.30%r0f cobalt alone in alloys used for forging.

Iron.lron is a normal impurity which may be tolerated in small amounts.It has no apparent efiect upon the alloy if present up to about 1%. Inamounts between 1% and 1.5 there is a tendency to embrittlement and lossof ductility. Not more than about 1.5% of iron can be tolerated. Itshould be kept around 0.20%.

Magnesium.-Magnesium, which has heretofore often been included inamounts of about 1.5 to 2% in aluminium base alloys, is according to thepresent invention regarded as an impurity to be kept as low as possible,

preferably below 0.20%, and preferably omitted altogethcr.

An example of an alloy especially suitable for casting, according to thepresent'invention, is as follows:

Aluminiumthe remainder (except for impurities).

This alloy when poured in an intricate mould possessed excellent castingqualities free of blow holes and shrinkage cavities. After the heattreatment above described it was found to have a stress-to-fracturecharacteristic (in hours at 300 C.) of about 4.3 long tons (9632 lbs.)per square inch.

Example 2 Percent Copper 5.5 Nickel 0.90 Titanium 0.21 Manganese 0.25iron trace Silicon 0.21 Cobalt 0.30 Antimony 0 Aluminium-4h: remainder(except for impurities).

Heat-treated as above, this alloy was found to have about the samestress-to-fracture characteristic as Example 1 above (that is, 4.3 longtons), and to possess good forging properties.

As a modification of the foregoing invention, small quantities ofzirconium, from about 0.03 to 0.40% (but in any event the total contentof zirconium plus titanium should not exceed about 0.50%), may be addedto the alloy. The preferred amount of zirconium is about 0.20%. By suchaddition, a substantial gain in stress-tofracture characteristic isachieved over the alloy hereinabove described. The use of zirconium has,however, certain disadvantages. It is diificult to remelt the stockingot material, apparently because complex compounds are formed whichare not readily soluble and hence the beneficial effects of this elementare lost. Zirconium should therefore be added to the ladle immediatelybefore casting. It appears to reduce slightly the castability of thealloy.

The following examples include zirconium:

Aluminium-the remainder (except for impurities).

After the heat-treatment above described, this alloy was found to havestress-to-fracture characteristics (in 100 hours at 300 C.) of about 5.5long tons (11,200 lbs.) per square inch. Its castability was not quiteas good as that of Example 1, but complex sand castings can neverthelessbe satisfactorily made of this alloy.

Example 4 Percent Copper 4.92 Nickel 0.94 Titanium 0.12 Manganese 0.25Iron trace Silicon 0.21 Cobalt 0.23 Antimony 0.16 Zirconium 0.07

Aluminium the remainder (except for impurities).

After the heat-treatment above described, this alloy was found to have astress-to-fracture characteristic, under the conditions stated, of about4.5 long tons (10,080 lbs.) per square inch, and to possess good forgingproperties.

What is claimed is:

1. A forgeable and castable alloy having a stress-tofracturecharacteristic in 100 hours at 300 C. in excess of 9000 pounds persquare inch, and consisting by weight of about 4.9% to 6.2% copper,about 0.90% to 1.2% nickel, about 0.10% to 0.25% titanium, about 0.20%to 0.30% manganese, about 0.20% to 0.30% cobalt and the balanceessentially aluminium.

2. A forgeable and castable alloy having a stress-tofracturecharacteristic in 100 hours at 300 C. in excess of 9000 pounds persquare inch, and consisting by weight of about 4.9% to 6.2% copper,about 0.90% to 1.2% nickel, about 0.10% to 0.25% titanium, about 0.20%to 0.30% manganese, about 0.20% to 0.30% cobalt, about 0.10% to 0.30%antimony, and the balance essentially aluminium.

3. A forgeable and castable alloy having a stress-tofracturecharacteristic in 100 hours at 300 C. in excess of 9000 pounds persquare inch, and consisting by Weight of about 4.9% to 6.2% copper,about 0.90% to 1.2% nickel, about 0.10% to 0.25% titanium, about 0.20%to 0.30% manganese, about 0.20% to 0.30% cobalt, about 0.03% to 0.40%zirconium, and the balance essentially aluminium.

4. A forgeable and castable alloy having a stress-tofracturecharacteristic in 100 hours at 300 C. in excess 6 of 9000 pounds persquare inch, and consisting by weight of about 4.9% to 6.2% copper,about 0.90% to 1.2% nickel, about 0.10% to 0.25% titanium, about 0.20%to 0.30% manganese, about 0.20% to 0.30% cobalt, about 0.10% to 0.30%antimony, about 0.03% to 0.40% zirconium, and the balance essentiallyaluminium.

5. An alloy useful for casting and having a stress-tofracturecharacteristic in hours at 300 C. of about 4.3 long tons per squareinch, consisting by weight of about 4.75% copper, about 1% nickel, about0.20% titanium, about 0.25% manganese, iron and silicon each notexceeding about 0.20%, about 0.25% cobalt, about 0.25% antimony, and thebalance essentially aluminium.

6. An alloy useful for forging and having a stressto-fracturecharacteristic in 100 hours at 300 C. of about 4.3 long tons per squareinch, consisting by weight of about 5.5% copper, about 0.90% nickel,about 0.21% titanium, about 0.25% manganese, about 0.21% silicon, about0.30% cobalt, and the balance essentially aluminium.

7. An alloy useful for casting and having a stress-tofracturecharacteristic in 100 hours at 300 C. of about 5.5 long tons per squareinch, consisting by weight of about 4.75% copper, about 1% nickel, about0.20% titanium, about 0.25% manganese, iron and silicon each notexceeding about 0.20%, about 0.25% cobalt, about 0.25% antimony, about0.20% zirconium, and the balance essentially aluminium.

8. An alloy useful for forging and having a stress-tofracturecharacteristic in 100 hours at 300 C. of about 4.5 long tons per squareinch, consisting by weight of about 4.92% copper, about 0.94% nickel,about 0.12% titanium, about 0.25% manganese, about 0.21% silicon, about0.23% cobalt, about 0.16% antimony, about 0.07% zirconium, and thebalance essentially aluminium.

9. A forgeable and castable alloy having a stress-tofracturecharacteristic in 100 hours at 300 C. in excess of 9000 pounds persquare inch, and consisting by weight ofabout 3.5% to 7% copper, about0.5% to 2% nickel, about 0.10% to 0.30% titanium, about 0.20% to 0.60%manganese, about 0.20% to 0.50% cobalt and the balance essentiallyaluminium.

10. An alloy as described in claim 9 containing in replacement of a likeamount of aluminium about 0.10% to 0.50% antimony but in any event notmore than about 0.60% of cobalt plus antimony.

11. An alloy as described in claim 9 containing in replacement of a likeamount of aluminium about 0.03% to 0.40% zirconium, but in any event notmore than about 0.50% of zirconium plus titanium.

12. An alloy as described in claim 9 containing in replacement of a likeamount of aluminium about 0.10% to 0.50% antimony and about 0.03% to0.40% zirconium, but in any event not more than about 0.60% of cobaltplus antimony and not more than about 0.50% of zirconium plus titanium.

References Cited in the file of this patent UNITED STATES PATENTS1,813,850 Hall July 7, 1931 1,932,851 Dean Oct. 31, 1933 2,063,942 NockDec. 15, 1936 2,131,520 Nock Sept. 27, 1938 2,254,202 Barnes Sept. 2,1941 2,381,219 Le Baron Aug. 7, 1945 2,459,492 Bradbury Ian. 18, 1949

9. A FORGEABLE AND CASTABLE ALLOY HAVING A STRESS-TOFRACTURECHARACTERISTIC IN 100 HOURS AT 300*C. IN EXCESS OF 9000 POUNDS PERSQUARE INCH, AND CONSISTING BY WEIGHT OF ABOUT 3.5% TO 7% COPPER, ABOUT0.5% TO 2% NICKEL, ABOUT 0.10% TO 0.30% TITANIUM, ABOUT 0.20% TO 0.60%MANGANESE, ABOUT 0.20% TO 0.50% COBALT AND THE BALANCE ESSENTIALLYALUMINUM.